This invention relates to an improved sealing strip for use with an encapsulated measuring device of the type used to measure the relative position of first and second objects, which device includes a housing adapted to be coupled to the first object and defining a slit which extends along a measuring direction, a follower adapted to be coupled to the second object and extending through the slit into the housing, and a measuring component disposed within the housing and coupled to move with the follower.
German Patent No. 28 46 768 discloses an encapsulated length measuring device in which a scale and a scanning unit are accommodated within a housing. This housing defines a through slit which extends along the measuring direction and is closed by means of sealing elements which are arranged in a roof-like pattern and which in the disclosed embodiment take the form of plastic or rubber lips. A follower extends between the lips through the slit and serves to connect the scanning unit with an object, the position of which is to be measured.
In the aforementioned measuring device, the sealing lips must lie closely against the follower if effective shielding or sealing is to be obtained. Therefore, the sealing lips are often constructed of elastic materials having high restoring forces in order to obtain and desired sealing effect. In consequence of the mechanical properties of the materials used for the lips, frictional forces on the follower are generated by the restoring forces. As the follower moves along the measuring direction, it can be deformed by these frictional forces. Of course, such deformations are detrimental to measuring accuracy. Furthermore, because the sealing lips are bent open by the follower, it is not unusual for twists to develop along the lengthwise extent of the sealing lips. For this reason, even when the follower is provided with a sword-shaped cross-section, small zones at the ends of the follower which are not adequately closed by the sealing lips are not uncommon.